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+An unnecessary type or const parameter was given in a type alias.
+
+Erroneous code example:
+
+```compile_fail,E0091
+type Foo<T> = u32; // error: type parameter `T` is unused
+// or:
+type Foo<A,B> = Box<A>; // error: type parameter `B` is unused
+```
+
+Please check you didn't write too many parameters. Example:
+
+```
+type Foo = u32; // ok!
+type Foo2<A> = Box<A>; // ok!
+```